This invention relates to buoyancy assemblies for attachment to a marine riser of the type used in off-shore drilling operations and extending between the drilling vessel and the wellhead on the ocean floor. It is well known in the art that a riser pipe that is tensioned upwardly tends to remain more nearly vertical and many drilling vessels include means for applying upward tensioning forces to the upper end of the riser. It is also common practice to apply buoyancy modules to the outside of the riser pipe to counteract its weight when submerged.
These techniques are generally discussed in "Deepwater Floating Drilling Operations" (1979), by L. M. Harris, The Petroleum Publishing Company, Tulsa, Okla., see Chapter 13 beginning on page 169. The prior patented art includes various buoyancy assemblies, such as disclosed in U.S. Pat. No. 3,705,432 to Watkins, and in U.S. Pat. No. 3,729,756 to Cook et al., both of which show semiannular flotation modules that are clamped together to substantially surround a riser pipe, providing support also for choke and kill lines. The parts of these modules are moulded together, however, making it impossible to replace damaged buoyant foam members per se while leaving the clamping and line supporting structures still attached to the riser pipe.
The prior art also shows strap tensioners comprising metal tension bars passed through loops in the strap and tensioned by adjustable bolt means, as disclosed in U.S. Pat. No. 4,128,921 to Heinze.